Lignocellulose is essentially composed of cellulose and hemicellulose and is the most abundant natural resource in the nature. Cellulose is insoluble in water, fibrous, and tough. Cellulose is a long-chained substance composed of 10,000 to 15,000 glucose molecules. The glucose molecules of cellulose are linked together by β-1,4 glucosidic bonds, and the β-1,4 glucosidic bonds are bonded to each other by hydrogen bonds, thereby allowing cellulose to take on a close-knit meshy structure. Most creatures, including human beings, are unable to make good use of cellulose-containing substances and use it as a carbon source directly. As a result, the unusable cellulose-containing substances fall within the categories of major sources of wastes, and some of them even pose adverse effects. For example, grains contain lignocellulose which encloses starch and therefore forms aggregates, and in consequence it not only compromises fodder on which poultry and livestock feed but also causes environmental pollution.
Cellulose hydrolase is a collective term that refers to a group of hydrolases which are, through coordinated synergetic effects thereof, capable of converting insoluble cellulose into monosaccharides by hydrolysis such that cellulose can be readily available for use by biological creatures. Depending on the characteristics and mechanism of the enzymes, cellulose hydrolases are of three types. The first type of cellulose hydrolases are known as exo-cellulose hydrolases or cellobiohydrolase. The second type of cellulose hydrolases are known as endo-cellulose hydrolases. The third type of cellulose hydrolases are known as cellobiohydrolase. Cellulose hydrolase-containing additives are added to the fodder to effectively eliminate the nutrient-related barrier caused by cellulose.
In recent years, due to the high speed at which energy resources are exploited and global warming develops, biomass energy is regarded as one of the forms of renewable energy. Take bioethanol as an example, it is added to gasoline to reduce gasoline consumption. Cellulose, a product of polymerization of glucose, is the most abundant organic matter in the world. If cellulose is properly decomposed and utilized, it will not only become a source of a tremendously great amount of biomass energy but also prevent a food crisis which might otherwise arise from keen competition among human beings for foods. Normally, conversion of cellulose into ethanol takes place in three steps, that is, pretreatment, saccharification, and fermentation. Saccharification is aimed at decomposing cellulose into saccharides which can be fermented by microorganism. There are usually two ways of performing saccharification, namely acid hydrolysis and enzyme hydrolysis. Acid hydrolysis not only produces substances, such as furfural and p-hydroxybenzoic acid, which inhibit subsequent fermentation, but is also harmful to an operating worker and the environment. By contrast, enzyme hydrolysis is the preferred option.
Enzyme-based saccharification requires a large amount of cellulose hydrolase. Therefore, cellulose hydrolase accounts for a major cost of bioethanol production. That is to say, a highly efficient cellulose hydrolase is the key to the development of the bioethanol industry. Orpinomyces sp. is a cellulose-utilizing strain that draws increasing attention in recent years. Compared with other microorganism present in the rumen, Orpinomyces sp. is of the least quantity; for example, Orpinomyces sp. accounts for 8% of the microorganism in the rumen of sheep. Nonetheless, Orpinomyces sp. is capable of high-efficiency cellulose decomposition. Orpinomyces sp. plays a particularly important role when a host feeds on fibrous fodder. In addition to its evolutionary advantages, Orpinomyces sp. is proved, by plenty of research results, to be capable of decomposing cellulose by cellulose hydrolase better than frequently used trichoderma fungi by several times to several thousand times. Hitherto, research has shown that absolute anaerobic fungi are capable of decomposing crystalline cellulose better than Trichoderma reesei QM9414 fungi widely studied and applied to industrial production. Hitherto, the role played by Orpinomyces sp. in the rumen has not yet been directly verified. However, Orpinomyces sp. manifests activity of various plant cell wall structure polysaccharide hydrolases in vitro, including exoglucanase, exoglucanase, beta-glucosidase, xylanase, xylosidase, and pectinase. This indicates that Orpinomyces sp. is equipped with an encompassing enzymatic system for decomposing plant cell wall structure polysaccharides. In addition to displaying highly specific activity toward a single substrate, plenty of cellulose hydrolases derived from Orpinomyces sp. nowadays are multifunction enzymes which not only decompose lignin, β-glucan, and various forms of cellulose, but also efficiently decompose plant residue composed of different constituents.